ORGANIC AMENDMENTS FOR MITIGATING SOIL SALINITY IN RICE

Received 01 March, 2019 Accepted 20 April, 2019 Online 30 April, 2019


INTRODUCTION
Soil salinity is a major concern to agriculture all over the world because it affects almost all plant functions. Millions of hectares of land throughout the world are too saline to produce economic crops, and more land is becoming non-productive each year due to salinity build up. Approximately 7% of the world's land area, 20% of the world's cultivated land and nearly half of the irrigated land are affected by soil salinity (Zhu, 2001;FAO, 2008;Mali et al., 2012). In view of another projection, 2.1% of the global dry land agriculture is affected by salinity (FAO, 2008). The world population is increasing rapidly and may reach 6 to 9.3 billion by the year 2050 whereas the crop production is decreasing rapidly because of the negative impact of various environmental stresses; therefore, it is now very important to develop stress-tolerant varieties to cope with this upcoming problem of food security. In addition, increased salinity of arable land is expected to have devastating global effects, resulting in up to 50% land losses by the middle of the twenty-first century (Mahajan and Tuteja, 2005). Agriculture is the most important sector of Bangladesh's economy. Usually 30-50% yield losses occur depending on the level of soil salinity. Over 30% of the cultivable area of Bangladesh lies in the coastal and offshore zones. Out of 2.86 million hectares of coastal and offshore lands, about 1.06 million hectares are affected by varying degrees of salinity (SRDI, 2010). The area under salinity is increasing with time (from 0.83 m ha to 1.056 m ha in 36 years; SRDI, 2010) due to rise in sea water level with increased global temperature. These coastal saline soils are distributed unevenly in 64 upazilas of 13 coastal districts covering portions of 8 agro-ecological zones of the country. Increased soil salinity due to climate change would significantly reduce food grain production. However, about 20% peoples of Bangladesh are seriously affected by soil and water salinity in the coastal belt. Transplated aman rice is mainly grown in the saline areas but the yield is very low due to lack of salt-tolerant high yielding variety and inappropriate management practices. According to the IPCC (2007), crop production may fall by 10-30% by 2050 in Bangladesh due to climate change. Salt stress increases the accumulation of toxic ions such as Na + and Clin different plant parts, tissues, cells and cell organelles. Accumulation of excess Na + and Clcauses ionic imbalances that may impair the selectivity of root membranes and induce potassium deficiency (Gadallah, 1999). Excess Na + and Cllead to the appearance of symptoms like K + deficiency. The deficiency of K + initially leads to chlorosis and then causes necrosis (Gopal and Dube, 2003).
Soil salinization is a major process of land degradation that decreases soil fertility and crop productivity. There is a report that coastal regions of Bangladesh are quite lower in soil fertility (Haque, 2006;Kibria et al., 2015). Appropriate management strategies and techniques with suitable crop genotypes having higher yield potential could contribute to the improvement of crop production in the coastal areas of Bangladesh. Both organic and inorganic amendments are found to be effective in the amelioration of saline soils. The best means of maintaining soil fertility, productivity and salt tolerance could be through addition of organic manures. Various organic amendments such as farmyard manure, compost, poultry manure and mulch can be used for the amelioration of saline soils. Organic amendments improve physical, chemical and biological properties of soils under saline conditions. There are evidences that soil amendments with organic manures reduce the toxic effects of salinity in various plant species (Idrees et

Experimental site and soils
The experiments were carried out at the farmer's field of Botiaghata, Khulna belongs to the Agroecological Zone of the Ganges Tidal Floodplain (AEZ 13). Characteristically, the soil was silty clay loam having pH 6.7-7.2, EC 4.6-6.6 dS/m, CEC 23-26 meq/100 g soil and organic matter 0.71-0.84%. The experimental area is included into the tropical monsoon climate. There are three monsoon periods appear in this region. The monsoon period lasts from May to October. About 88% of the total rainfall is observed in this time. Hailstone also occurs during this time. Sometimes storms locally called Kalboishakhi are observed.

Plant materials and treatments
The experiment was laid out in a randomized complete block design (RCBD) with three replications. Two rice cultivars; BR-23 and local cultivar Mohini were used in aman season while BRRI dhan29 and BINA dhan-8 rice were used in boro season as test crops in the experiments. The treatments consisted with control and two doses of FYM and PM. There were five treatments namely T0= control (no manure), T1=FYM (5 t/ha), T2=FYM (10 t/ha), T3=PM (4 t/ha), and T4=PM (8 t/ha). Recommended doses of TSP, MoP, gypsum, and zinc sulphate were applied to all the experimental plots during final land preparation. Recommended dose of urea was applied in three splits. Thirty-day-old seedlings of four rice varieties were transplanted in the experimental plots. Three seedlings per hill were placed at a spacing of 25 cm × 20 cm. Water salinity was monitored during the whole period of crop cultivation. Water salinity during aman rice was 4.2 dS/m, 2.0 dS/m and 2.1 dS/m at seedling stage, tillering stage and panicle initiation stage, respectively. Water salinity during boro rice was 3.2 dS/m, 9.4 dS/m and 13.8 dS/m at seedling stage, tillering stage and panicle initiation stage, respectively. Other intercultural operations were done when necessary. The crop was harvested at full maturity. Maturity of crop was determined when about 90% grains became golden yellow. Grain and straw yields and plant parameters were recorded.

Chemical analysis of plant samples
The representative grain and straw samples were dried in an oven at 65 0 C for about 24 hours before they were ground by a grinding machine. The prepared samples were stored in paper bags and finally kept into desiccators until analysis. The N, P, K, S and Na contents from grain and straw samples were determined following standard method as described by Khanam et al. (2001).

Statistical analysis
Data were analyzed statistically using analysis of variance with the help of software package MSTAT-C. The significant differences between mean values were compared by Duncan's Multiple Range Test. Differences at P≤0.05 were considered significant.

Growth and yield components of rice
Soil salinity caused a significant decrease in plant height of four rice varieties viz. BR-23, Mohini, BRRI dhan29 and BINA dhan-8. Application of organic manures increased the plant height of four rice varieties under saline condition (Tables 1, 2, 3 and 4). Salinity significantly decreased effective tillers hill -1 of four rice varieties viz. BR-23, Mohini rice, BRRI dhan29 and BINA dhan-8 (Tables 1, 2, 3 and 4). Application of organic manures did not show significant increase in number of effective tillers of all rice cultivars. It was observed that there were no significant variations in panicle length of four rice varieties viz. BR-23, Mohini, BRRI dhan29 and BINA dhan-8 among the organic amendments. Plants exposed to salinity decreased the number of filled grains panicle -1 of four rice varieties (Tables 1, 2, 3 and 4). It was observed that number of filled grains panicle -1 in all varieties was significantly increased due to organic amendments under salinity condition. The 1000grain weight of all the varieties was also significantly decreased due to salinity (Tables 1, 2, 3 and 4). Application of organic manures increased 1000-grain weight but there were no significant differences among them.     Same letter in a column represents insignificant difference at p < 0.05. SE=Standard error of means, CV=Co-efficient of variation. Same letter in a column represents insignificant difference at p < 0.05. SE=Standard error of means, CV=Co-efficient of variation. Grain and straw yields Plants exposed with salinity significantly decreased grain yield of four rice varieties. Organic amendments with FYM and PM significantly increased grain yield of all rice varieties (Tables 5 and 6). Salt stress also significantly decreased straw yield of rice varieties whereas organic amendments significantly increased straw yield (Tables 5 and 6). Amanullah et al. (2007) have shown that organic and inorganic amendments enhanced the yield of rice against soil salinity. Shaaban et al. (2013) reported that FYM along with inorganic amendments increased the paddy yield in salt affected soil. Haq et al. (2001) reported that combined application of gypsum, pressmud and FYM produced the highest rice yield in a saline-sodic soil. There are evidences that organic manures reduce the adverse effects of various stresses on plants by affecting the uptake and accumulation of inorganic nutrients (Zaki et al., 2009. Abou El-Magd et al., 2008).

Nutrient uptake by rice
Soil salinity caused a significant decrease in N uptake by four rice varieties. Organic amendments significantly increased N uptake by four rice varieties under salinity condition. Salinity also caused a significant decrease in P uptake by four rice varieties. Application of FYM and PM increased P uptake by all rice varieties under salinity condition. Soil salinity caused a significant decrease in S uptake by four rice varieties. Organic amendments increased S uptake in four rice varieties under salt stress condition (data not shown).

K + /Na + ratio
Salinity caused significant decrease in K + /Na + ratio in both grain and straw of four rice varieties. Application of organic amendments significantly increased K + /Na + ratio in both grain and straw of all the varieties (data not shown). Similar to our results, Zaki et al. (2009) found that organic manure increased the NPK uptake and vegetative yield under saline conditions. It has been reported that salt stress causes increased uptake of Na + and Cl -, and decreased uptake of essential cations particularly K + (Khan et al., 2003). Similarly, Leithy et al. (2010) conducted an experiment to study the effect of saline water in addition to bio and organic fertilization treatment on geranium plant growth, mineral and chemical constituents. Salinity affected most of the morphological parameters and decreased the growth performance.

Post-harvest properties of saline soils
The findings also analyzed the post-harvest properties of saline soils. No considerable changes in postharvest soil properties such as pH, EC, CEC and organic matter status were observed by addition of organic manures (data not shown).

CONCLUSIONS
Soil salinity reduced the growth and yield of four rice varieties. BR-23 variety produced higher yield than local cultivar Mohini in aman season while BINA dhan-8 produced higher yield than BRRI dhan29 in boro season. Organic amendments with both FYM and PM resulted in significant increases in growth and yield of all rice varieties under salinity conditions. Salinity also caused a decrease in nutrient uptake and K + /Na + ratio in rice. Improved growth and yield of rice by organic amendments were accompanied with increased K + /Na + ratio and nutrient uptake under salinity conditions. It can be concluded that organic amendments with FYM and PM confer tolerance to salinity in rice due to increasing nutrient uptake and maintaining higher K + /Na + ratio. However, crop cultivation in saline areas might be profitable with organic amendment of soils. Extensive field research work is needed in this area since organic manures like FYM and PM are more available and less expensive.